In the LTE-A system, in order to increase the transmission rate at the cell edge, the 3rd Generation Partner Project (3GPP) sets forth the coordinated multi-point Transmission and Reception (CoMP) technology at the R11 stage, and this technology mainly increases the data transmission rate of edge users through inter-cell coordination. Although the CoMP technology improves the throughput of the edge users, it also increases complexity of the network system.
Within the same SRS bandwidth in the LTE system, SRS sub-carriers are spaced apart, that is, the SRS transmission uses the comb structure. The number of spectrum combs in the LTE system is 2, which also corresponds to the RePetition Factor (referred to as RPF) of 2 in the time domain. FIG. 1 is a schematic diagram of the SRS comb structure in the related art. Users only use sub-carriers whose frequency domain index is an even or odd number to transmit the SRS according to the instruction of the 1-bit upper layer signaling. This comb structure allows more users to transmit the SRS within the same SRS bandwidth.
In the same SRS bandwidth, multiple users use different cyclic shifts in the same frequency comb, and then send the SRS through code division multiplexing, or two users can transmit the SRS in different spectrum combs through frequency-division multiplexing. Specifically, in the LTE system, users transmitting the SRS within a certain SRS bandwidth (four resource blocks) can use eight cycle shifts and 2 spectrum combs, so that the users have a total of 16 resources to transmit the SRS. That is, up to 16 SRSs can be transmitted simultaneously in this SRS bandwidth. The LTE system only supports the SIMO (Single Input Multiple Output), therefore up to 16 users can be supported simultaneously, but the LTE-A system supports the MIMO (Multiple Input Multiple Output), therefore, only four users can be simultaneously supported for 4-antenna users.
Aiming to the problem of SRS resource shortage brought by multiple antennas, the LTE-A introduced the aperiodic SRS at the R10 stage. The aperiodic SRS improves flexible configuration and effective utilization of SRS resources through dynamical triggering, but it does not fundamentally improve the SRS resource capacity.
The 3GPP proposed a variety of scenarios for the CoMP technology, and in addition to the conventional homogeneous network scenarios, there are also heterogeneous network scenarios. In the heterogeneous network scenarios, especially in the fourth CoMP scenario, the macro cell and all micro cells under its coverage use the same cell identifier, and compared with the traditional networks, the number of users supported under the same cell identifier is greatly increased. At the R8/9/10 stage, the SRS resources are associated with cell identifiers, that is, although the existing SRS resources are sufficient for traditional cells in the R8/9/10, but for the R11 cells especially for the fourth CoMP scenario, it may be far from enough. Based on this requirement, many technologies are proposed to extend the SRS comb, by expanding the spacing of SRS subcarrier, the original two comb values (RPF=2) are extended to four comb values (RPF=4). The comb extension can effectively increase the SRS capacity, and the related art also proves that the extended SRS channel detection performance degradation is in the acceptable range, but the backward compatibility problem is one of the key issues deciding whether it can be adopted by the LTE standard in the future or not.